Real-Time Simulation Workflow

The figure shows the real-time simulation workflow. The connectors
are exit points for returning to the real-time model preparation workflow.

The figure shows the real-time model preparation workflow. The
connector is an entry point for returning to the real-time model preparation
workflow from other real-time workflows (for example, the real-time
simulation workflow or the hardware-in-the-loop simulation workflow).

Use the real-time simulation workflow to increase the likelihood
that your model is real-time capable. Your model is real-time capable
if it meets both of these criteria when you simulate it on your real-time
computer:

The results match your expectations, based on empirical
data or theoretical models.

The model simulates without incurring an overrun.

The real-time simulation workflow uses bounded, that
is fixed-step, fixed-cost, simulation. Fixed-step, fixed-cost simulation
sets an upper boundary on computational cost by limiting both the
step size and the number of iterations that the solver uses.

Evaluate Model Accuracy

Compare the results from the simulation on the target computer
to your reference results. Are the reference and modified model results
the same? If not, are they similar enough that the empirical or theoretical
data also supports the results from the simulation of the modified
model? Is the modified model representing the phenomena that you want
it to measure? Is it representing those phenomena correctly? If you
plan on using your model to test your controller design, is the model
accurate enough to produce results that you can rely on for system
qualification? The answers to these questions help you to decide if
your real-time results are accurate enough.

Improve Accuracy by Adjusting Solver Settings

If your fixed-step, fixed-cost simulation results do not match
your reference results, try to improve accuracy by adjusting solver
configurations. Increasing the number of iterations or decreasing
the step size can improve accuracy.

For an implicit global solver (ode14x, ode1be), increase the number of Newton’s iterations.
For a Backward Euler or Trapezoidal Rule local solver, increase the number of
nonlinear iterations.

For the global solver, and for any local solvers, decrease the
step size. Configure the step size for each local solver as an integer
multiple of the step size you specify for the global solver.

Return to the Real-Time Model Preparation Workflow

If changing solver configurations does not improve or speed
enough, try to make your model real-time capable by returning to the
real-time model preparation workflow.

Adjust the fidelity or scope of your model, and then step through
the other processes and decisions in the real-time model preparation
workflow. Iterate on adjusting, simulating, and analyzing your model
until it is fast and accurate enough for you to attempt the real-time
simulation workflow again. For information, see Real-Time Model Preparation Workflow.

Evaluate Overrun Risk

In terms of speed, the only method for definitively determining
that your model is real-time capable is to test for overruns during
simulation on your target hardware. You can, however, use fixed-step,
fixed-cost simulation to estimate the likelihood that your solver
executes quickly enough for real-time simulation. For information
on estimating simulation time, see Estimate Computation Costs.

Improve Simulation Speed by Adjusting Solver Settings

If your computational cost estimate indicates that your model
executes too slowly to avoid an overrun on a real-time target machine,
try to increase simulation speed by adjusting solver configurations.
Decreasing the number of iterations or increasing the step size can
improve accuracy.

For an implicit global solver (ode14x, ode1be), decrease the number of Newton’s iterations.
For either a Backward Euler or Trapezoidal Rule local solver, decrease the
number of nonlinear iterations.

For the global solver, and for any local solvers, increase the
step size. Configure the step size for each local solver as an integer
multiple of the step size you specify for the global solver.

Model Is Real-Time Viable

When fixed-step, fixed-cost simulation results indicate that
your model is likely real-time capable, you can attempt real-time
simulation on the target hardware. For information on how you can
use real-time simulation to test your controller hardware, see What Is Hardware-In-The-Loop Simulation?.

Return to the Real-Time Simulation Workflow

The connector is an entry point for returning to the real-time simulation
workflow from another workflow (for example, the hardware-in-the-loop simulation
workflow).

Insufficient Computational Capability for Real-Time Viability

It is possible that your real-time target machine lacks the
computational capability for running your model in real time. If,
after multiple iterations of the workflow, there is no combination
of model complexity and solver settings that makes your model real-time
viable, consider these options for increasing processing power:

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